Relativistic Defense Force
I really need a name for this, but the relativistic defense force is in place to protect the earth and nearby planets protected from relativistic kinetic kill vehicles, especially those used by civilians. It has several layers of defense. Traffic Control Any ship coming in through warp reports to traffic control when it enters the system. Warp entry is less like sneaking into a system through an open window and more like kicking down the door to the reality. Shouting "Honey I'm home," to the local traffic control is the best way to avoid having a naval patrol ship ask you some pointed questions, as in, questions with rail guns pointed at you. Warp entry and exit points are all located a predictable distance from the local massive gravity well, in this case the sun. As such, they are easily monitored and patrolled. All ship travel within the solar system is monitored by traffic control for a variety of reasons. Ensuring none attempt relativistic velocity within the system is just one of those. Travel between solar systems is rare, perhaps 2 or 3 flights per year. All such flights require an extensive licensing process to ensure that the ship is going for legitimate scientific research purposes, and not in an attempt to destroy the earth. (Also, it's essentially impossible to warp to a star near Earth or anywhere else within, say 100 light years, that's in near the closely monitored section near the sun.) Relativistic Pursuit Craft Should a ship attempt to leave the solar system without authorization, they are assumed to be attempting a relativistic attack on earth. To prevent this, several interceptor vessels are kept ready at all times to hunt down and destroy such ships. These ships are designed around accelerating as fast as possible with a single laser cannon to shoot down threatening ships. With the introduction of Turgons into the alliance, one ship is specifically crewed by Turgons alone, allowing it to reach faster accelerations than humans could bear. However, the other ships are crewed by a mixture of races, on the suspicion that perhaps the Turgons might choose to launch an attack. While the crews are closely vetted for loyalty, when it comes to the destruction of Earth, no chances are taken. Interdiction Efforts Should the pursuit craft fail to destroy the relativistic kinetic kill vehicle, it will report the location back to Earth. Earth will then scramble defenses to intercept the craft before it's too late. The primary means of interception are interdictor torpedoes. These torpedoes are essentially nuclear warheads used to disperse massive amounts of sand through a huge volume of space. If the sand is interposed between the earth and the RKKV, a single grain should be enough to destroy the craft. Earth's exact supply of these torpedoes is unknown, but rumored to be in the millions. Navy RKKV's Rumors abound of the navy possessing RKKV's of their own. While these are closely guarded secrets, most people believe the navy has at least a few of these. As of yet they have not seen use in warfare. The main reason is that planets that support life are rare and valuable, and destroying them is a Pyrrhic victory at best and a war crime at worst. Planets that cannot support life are sparsely populated, and RKKV's are overkill when a handful of nukes can accomplish the job at a lower cost and with much greater precision. The truth is simply that RKKV's are simply incompatible with most military engagements, which rely on judicious use of force rather than complete extermination of a population.